1. Technical Field
The present invention relates to a shaft rotation type linear motor unit that can apply a rotary movement and a linear movement to an object to be driven.
2. Description of Related Art
A linear motor is small in size and operable at high speed compared with mechanical actuation such as a ball screw mechanism since it operates by electromagnetic induction. For example, a rod type linear motor is used for a chip mounter (an electronic component mounting device) of a semiconductor manufacturing device.
The rod type linear motor includes a rod that includes permanent magnets and coils that surround the rod, and applies a thrust in the axis direction to the rod by using electromagnetic induction of a magnetic field of the permanent magnets and an electric current flowing in the coils so that the rod performs a linear movement.
Recently, a number of technique has been proposed for achieving a torque generator of a rotary motor and a thrust generator of a linear motor by devising a connecting mechanism of a ball spline and a bearing so as to perform a rotary movement and a linear movement.
As a technique for a linear motor that can perform a rotary movement and a linear movement, Japanese Patent No. 3300465 discloses an actuator with two degree of freedom which includes a rotary motion shaft having a linear shaft portion and a spline groove on part of the outer periphery of the rotary motion shaft, and a spline guide bearing that engages with the spline groove of the rotary motion shaft.
Further, Japanese Unexamined Patent Application. Publication No. 2010-57357 discloses a linear actuator which includes a second shaft member arranged in parallel with a rod of a linear motor. According to Japanese Unexamined Patent Application Publication No. 2010-57357, the distal end of the rod and the distal end of the second shaft member are connected by a first connecting member so that the second shaft member performs a linear movement as the rod performs a linear movement. The second shaft member and a housing are connected by a second connecting member so that the second shaft member can perform a linear movement and is prevented from being rotated about the axis of the rod.
According to the technique of Japanese Patent No. 3300465 and Japanese Unexamined Patent Application Publication No. 2010-57357, the connecting mechanisms are complicated, and therefore, the linear motor may not accommodate size reduction, space saving and weigh reduction.
Recently, a small-sized linear motor is developed which includes a center shaft for a linear movement configured to be unrotatable and an additional rotation shaft arranged in parallel with the center shaft so that the rotation shaft is rotatable in accordance with the movement of the center axis. However, the small-sized linear motor which includes the center shaft and the rotation shaft also needs a connecting section of the center shaft and the rotation shaft. Accordingly, it is disadvantageous for size reduction, space saving and weigh reduction of the linear motor.